This invention relates to a method of chlorinating and brominating aromatic compounds. In particular, it relates to a method of chlorinating and brominating aromatic compounds under pressure using only a catalytic amount of a Lewis acid catalyst.
Aromatic compounds, such as methyl4methylbenzoate (M4MB), are commonly chlorinated at atmospheric pressure using chlorine gas in the presence of a Lewis acid catalyst, such as aluminum chloride, AlCl.sub.3, or ferric chloride, FeCl.sub.3. The amount of Lewis acid catalyst used must be greater than stoichiometric to effect the chlorination. For example, 0.98 lbs. (1.1 equivalents) of aluminum chloride are required to chlorinate each pound of M4MB.
After the reaction is complete, separation of the catalyst from the product by filtration or distillation is impractical or not possible because the catalyst is chemically bound to the product. The usual procedure is to add water, causing the catalyst to react with the water to form a soluble product. For example, an aluminum chloride catalyst reacts with water to form hydrochloric acid and aluminum hydroxide, which dissolve in the water and can be separated from the solid product.